Date: Tue, 25 Nov 2014 00:59:40 -0700 From: Warner Losh <imp@bsdimp.com> To: Mark R V Murray <mark@grondar.org> Cc: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no>, Ian Lepore <ian@FreeBSD.org>, arch@freebsd.org Subject: Re: svn commit: r274739 - head/sys/mips/conf Message-ID: <4DC9E093-C877-40D4-A998-2C94318FECA6@bsdimp.com> In-Reply-To: <B7727BFD-FBEC-4574-8382-7A00AF6D27AF@grondar.org> References: <201411200552.sAK5qnXP063073@svn.freebsd.org> <20141120084832.GE24601@funkthat.com> <AE8F2D30-7F91-4C90-B79A-D99857D8AED8@grondar.org> <20141121092245.GI99957@funkthat.com> <1416582989.1147.250.camel@revolution.hippie.lan> <026FEB8A-CA8C-472F-A8E4-DA3D0AC44B34@grondar.org> <1416596266.1147.290.camel@revolution.hippie.lan> <F017033A-B761-4435-A7F8-264D2F4662A0@grondar.org> <1416598889.1147.297.camel@revolution.hippie.lan> <86egsvueqk.fsf@nine.des.no> <1416691274.1147.339.camel@revolution.hippie.lan> <398A380D-49AF-480C-8842-8835F81EF641@grondar.org> <1416806894.1147.362.camel@revolution.hippie.lan> <18B8A926-59C0-49B4-ADA3-A11688609852@grondar.org> <1416841268.1147.386.camel@revolution.hippie.lan> <CC6B67E1-55A2-4952-AB43-5F6C787F629B@grondar.org> <86wq6k9okk.fsf@nine.des.no> <4C2BD093-BEA2-47F9-B575-90342712E9B2@bsdimp.com> <B7727BFD-FBEC-4574-8382-7A00AF6D27AF@grondar.org>
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--Apple-Mail=_194AE083-21C7-43E7-BD0E-386E833EAC1E Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Nov 25, 2014, at 12:57 AM, Mark R V Murray <mark@grondar.org> = wrote: >=20 >=20 >> On 24 Nov 2014, at 23:22, Warner Losh <imp@bsdimp.com> wrote: >>=20 >> What=E2=80=99s the minimum specs required for get_cyclecount()? Not = all of the >> boxes that Ian was posting about have high-resolution time-keeping = counters >> in hardware=E2=80=A6 Maybe there=E2=80=99s some underlying = expectation for this function >> that these systems either aren=E2=80=99t providing or can=E2=80=99t = provide. >=20 > get_cyclecount should be a high-resolution timing counter linear in = time, with a minimum tick no more accurate than a single instruction = execution. In practice we take what we can get. It is used to measure = hopefully chaotic events in order to obtain environmental entropy. So right. armv6 and mips have something akin to that, but IIRC, not all = arm v4/5 boxes can do much better than microseconds=E2=80=A6 Warner --Apple-Mail=_194AE083-21C7-43E7-BD0E-386E833EAC1E Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJUdDbtAAoJEGwc0Sh9sBEArCkP+wf+vA3VfAeJdNzdxB36gH8V XTfdstgV6flM723BaurBHy187uqHhZP4GMVhvdIRvIKO7xYYOPm6Vk2bxZZ5Nexv 5mDN2bgOWiPMB0h68sm8nmsno2U/0tcbK+DWEVBwDIsMB/IYYTByl98nH90oyVDk lgVUeM5SQ0FRTyH1VRL5txRTHE1WrvC7jtCyLTjIHCnHMYSAUbd0R++EYVmSvWHV 1aANPADhrDX9DWnhytw/Dxj4C/6FA6dWNRcCc/BW9eZUrUOneo/LUX0EXNE5xnTu SaUrZQxXThDVgCbExtB7OPKJ9/liigtcQMxR0MNoJaNlqmNwZW6xiVKSEXAVCKNR 7gUQFG29k2eQrB/XYbAF8xkSWbZXyHYzXpUHpTQd6CdHgRHfw4AtppZF+w0YvSLn zINTGEBH8EQEf90Y+e7wZnhC01OCPYFk5LH/4p32IbCYXkkMKB/iMbbdMXZQ0Hnu E59rl0M0UWRWQksdD4YwiZegynk1fyjJR2IcP8Aa8CIe3xwlniuMF59RLrqFy21S Qj6j9ysH9QGwvAt1qXRj3lzznly4nLLfvU9RkhAydWOX9DH8NdViL/uy65l/u12T Xe0yBWp9fsE+NC9fPvA9haxsYTMpyvBF1gIxk0GDBfrX9m7hKEODnN1Tkk9UZY/r 6KA8jzwxFNiP9CFrZf45 =ffoI -----END PGP SIGNATURE----- --Apple-Mail=_194AE083-21C7-43E7-BD0E-386E833EAC1E--
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